High sensitivity detection of magnetic fields is critical to many applications including ordinance detection, geophysical mapping, navigation, and the detection of biomagnetic fields associated with heart and brain activity. Conventional superconducting magnetometers based on superconducting quantum interference devices (SQUIDs) provide a high sensitivity for magnetic field detection but are bulky and require expensive cryogenic cooling. Atomic magnetometers, which are based on optical measurements of an unpaired electron spin in an alkali metal vapor are being developed. These atomic magnetometers do not require cryogenic cooling; and they are capable of measuring the absolute magnetic field at high sensitivity (down to less than one femto Tesla).
The present invention provides an advance in the art of atomic magnetometers by providing an atomic magnetometer which can be formed, at least in part, by micromachining.
The atomic magnetometer of the present invention also provides a new method and apparatus for detecting magnetic fields by utilizing an optical cavity formed by a transmission grating and a mirror which are spaced about a vapor cell containing an alkali metal vapor. The effect of a magnetic field on the alkali metal vapor is to change an effective index of refraction within the optical cavity of the present invention. When a probe laser beam is coupled through the transmission grating into the optical cavity, a diffracted laser beam is generated as the probe laser beam is coupled out of the optical cavity through the transmission grating; and this can produce a zeroth-order component and a first-order component in the diffracted laser beam. By measuring these components of the diffracted laser beam with separate photodetectors in the apparatus of the present invention, electrical signals can be generated from the photodetectors which can be used to determine the intensity of the magnetic field.
These and other advantages of the present invention will become evident to those skilled in the art.